Sensor

ABSTRACT

A measurement sensor for determining a physical property of a measurement gas, e.g., the concentration of a gas component or the temperature of a measurement gas, in particular of the exhaust gas of internal combustion engines, has a housing and a sensor element accommodated in the housing. The sensor element has an end segment at the measurement gas side that protrudes from the housing and a connection-side end segment that bears at least one contact surface. The sensor element also has at least one conductor element that contacts the at least one contact surface. In order to achieve low transition resistances at the electrical contacting and a decoupling from mechanical stress, the contact surface and the conductor element are connected to one another by welding, and are embedded in a ceramic compound at least in the area of the welded connection.

FIELD OF THE INVENTION

The present invention relates to a measurement sensor for determining aphysical property of a measurement gas, e.g., the concentration of a gascomponent or the temperature of a measurement gas, e.g., of the exhaustgas of internal combustion engines.

BACKGROUND INFORMATION

In a known gas measurement sensor described, for example, in publishedGerman patent document DE 101 32 828, the contacting between the atleast one contact surface and the at least one conductor element iscreated by a contact holder that uses a spring element to press the atleast one conductor element onto the contact surface. The at least oneconductor element is connected via a crimp connection to a connectingline with which the sensor element can be connected to an electroniccontrol device, as described, for example, in published German patentdocument DE 195 42 650.

SUMMARY

The measurement sensor according to the present invention has theadvantage that the welded connection ensures an optimal electricaltransition impedance and enables economical manufacture. Through itsembedding in an insulating ceramic compound, the welded connection ismechanically decoupled and is therefore not sensitive to vibrationalstresses that can occur if the measurement sensor is used as an exhaustgas sensor in internal combustion engines in vehicles. As a result ofthe greater mechanical strength of the measurement sensor thus achieved,its useful life is significantly extended. The embedding can be achievedby pressing in or encapsulation with an insulating compound, or by apowder filling.

According to an example embodiment of the present invention, the ceramiccompound is brought into the housing during the lining of themeasurement sensor, as a compressed powder filling, and fills the spacebetween the sensor element and the inner wall of the housing. Magnesiumoxide (MgO) may be used as the powder material. For the pressing in orencapsulating, a ceramic casting compound may be used. Alternatively,ceramic glue, steatite, or aluminum oxide (Al₂O₃) can also be used.

According to an example embodiment of the present invention, the weldedconnection is created by resistance welding. The welding of theconductor element, which may be made of nickel (Ni), to the contactsurface, e.g., made of platinum or a platinum cermet, can however alsobe carried out using a welding laser.

According to an example embodiment of the present invention, a counterdisk that spans the housing cross-section is fixed in the housing, andthe at least one conductor is led through this counter disk. A sealingpiece that fills the housing cross-section and that has a feedthroughthat surrounds the sensor element in the area of the welded connectionis pressed into the housing, and the intermediate space between thecounter disk and the sealing piece, as well as between the sensorelement and the wall of the feedthrough, is filled completely with aceramic casting compound and/or a ceramic glue. This example embodimenthas the advantage that even given a miniaturization of the measurementsensor the addition of the ceramic casting compound or of the ceramicglue results in an optimal insulating binding of the welded connectionand an optimal gas-tight sealing of the sensor element. Here theintroduction of the ceramic casting compound or of the ceramic glue isvery simple, because the position of the filling support does not haveto be very precise. The ceramic casting compound or the ceramic glue canbe filled with a high tolerance as to quantity, because when the sealingpiece is pushed in via the feedthrough in the sealing piece, excesscompound is pressed out of the intermediate space between the sealingpiece and the counter disk, and can be removed at the exposed end of thesealing piece if necessary. The quality of the seal can also be assessedon the basis of the quantity of ceramic casting compound or ceramic glueexiting the feedthrough. Because the ceramic casting compound or theceramic glue both seals the welded connection to the sealing piece andalso seals the intermediate space between the sealing piece and thecounter disk to the housing, the conventional sealing packing of twosteatite disks with a boron nitride disk situated between them can beomitted, so that a construction of the measurement sensor that is shortin the axial direction may be achieved. However, such a sealing systemis to be provided in the cases in which the sensor element is to beadditionally held, for example in order to avoid vibrational movementsof the sensor element.

According to an example embodiment of the present invention, thefeedthrough provided in the sealing piece for the sensor element has inthe area of the welded connection an inner cross-section that is matchedto the cross-sectional shape of the sensor element, the innercross-section decreasing continuously as it extends from the end surfacefacing the counter disk to the end surface of the sealing piece facingaway from the counter disk. In the distribution of the ceramic castingcompound and/or of the ceramic glue brought about by pushing in thesealing piece, this tapering of the feedthrough has a throttling effect,so that the ceramic casting compound or ceramic glue is firstdistributed radially in uniform fashion, and is then increasinglypressed out through the feedthrough as the sealing piece is pressedfurther in.

The pre-assembly of the measurement sensor for creating the gas-tightrouting of the at least one conductor connected to the sensor elementout of the housing takes place in the following method steps:

The counter disk through which the at least one conductor element is ledis fixed in the housing, the sealing piece is placed on the sensorelement, the end of the sensor element is inserted into the blind holeof the counter disk, and the at least one conductor element protrudingfrom the counter disk is welded to a contact surface on the sensorelement. A determined quantity of ceramic casting compound and/orceramic glue is now dispensed onto the counter disk, and the sealingpiece on the sensor element is pushed towards the counter disk untilbetween the end surface of the sealing piece and the counter disk thereremains only a small intermediate space, whose minimum axial depth isdetermined by the spacer piece provided on the sealing piece. In thisintermediate space between the sealing piece and the counter disk, theceramic casting compound or the ceramic glue seals the sealing piece andcounter disk against the housing. The blind hole of the counter disk hasa through hole to the cable harness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a segment of a longitudinalsection of a measurement sensor.

FIG. 2 shows a cross-sectional view of a segment of a longitudinalsection of the measurement sensor according to a second exemplaryembodiment.

FIG. 3 shows a perspective view of a sealing piece of the measurementsensor shown in FIG. 2.

DETAILED DESCRIPTION

The measurement sensor according to the present invention, of which asegment is shown in longitudinal section in FIG. 1, is used to determinea physical property of a measurement gas.

Such a property is for example the concentration of a gas component orthe temperature of the measurement gas. As an example, this measurementsensor is used in internal combustion engines in vehicles as an exhaustgas sensor that measures either the concentration of oxygen in theexhaust gas of the internal combustion engine (lambda sensor) or thetemperature of the exhaust gas (temperature sensor).

The measurement sensor has a housing 11 that accommodates a sensorelement 12 that protrudes with a measurement-gas-side end segment fromhousing 11 and is exposed to the measurement gas. On an end segment 121at the connection side, sensor element 12 has, on surfaces facing awayfrom one another, a plurality of contact surfaces 13 made of platinum orof a platinum cermet that are connected to electrical printed conductors(not shown here) that lead to the measurement-gas-side end segment. Inthe exemplary embodiment, two of these contact surfaces 13 are shown.Sensor element 12 is led through a sealing system 17 that is situatedbetween the two end segments and that supports sensor element 12 onhousing 11 and mechanically dampens its vibrations, as well as sealingconnection-side end segment 121 against the measurement gas. Sealingsystem 17 is made of two ceramic shaped parts 14 and 15, e.g., made ofsteatite, that clamp between them a sealing element 16, made, e.g., ofboron nitride.

For connecting sensor element 12 to an electronic control device, eachcontact surface 13 is contacted by a conductor element 18 that is routedto a connecting plug that is connected to the connecting line to theelectronic control device, as described, for example, in publishedGerman patent document DE 195 23 911. Conductor element 18 may be madeof nickel (Ni). In order to create an electrical contacting with minimaltransition impedances, conductor elements 18 are welded to theirallocated contact surfaces 13; resistance welding may be used as awelding method, but laser welding can also be used.

In the installation of sensor element 12 in housing 11, in the area ofthe welded connections sensor element 12 is embedded in a ceramiccompound 19 that surrounds the connection-side end segment 121 of sensorelement 12 and is supported on the inner wall of housing 11. In theexemplary embodiment, the embedding is made in a compressed,high-temperature-resistant powder filling that completely fills thespace between the connection-side end segment 121 of sensor element 12and the inner wall of housing 11 up to sealing system 17. As a powder,magnesium oxide (MgO) may be used. However, the embedding in ceramiccompound 19 can also take place through encapsulation or pressing in. Inthis case, a ceramic casting compound, a ceramic glue, or steatite oraluminum oxide (Al₂O₃) is used as a material.

Ceramic compound 19 is covered at one end of the housing by aninsulating disk 20 that is supported peripherally on the inner wall ofhousing 11, through which conductor elements 18 are led. Insulating disk20 may be made of aluminum oxide. At its end, housing 11 is crimped ontoinsulating disk 20, so that insulating disk 20 is axially fixed. On theside of sealing system 17 facing the measurement-gas-side end segment,an additional insulating disk 21 is situated that surrounds sensorelement 12 and lies peripherally against the inner wall of housing 11.

Because insulating ceramic compound 19 also has a sealing function andseals connection-side end segment 121 of sensor element 12 against theexhaust gas, in the case in which ceramic compound 19 is not thedescribed powder filling but rather a press compound or castingcompound, sealing system 17 can be realized in simplified fashion, forexample by omitting components 15 and 16 of sealing system 17.

According to another exemplary embodiment, the measurement sensor ofwhich a segment is shown in longitudinal section in FIG. 2 has a housing11 into one end of which a tube-shaped, possibly flexible connectingpiece 23 is pushed, in which conductor elements 18 are led to aconnecting plug that terminates connecting piece 23. A counter disk 24is placed into connecting piece 23 with an axial distance from the tubeend penetrating into housing 11 of this connecting piece, and conductorelements 18 are led through this counter disk. As in the exemplaryembodiment of FIG. 1, conductor elements 18 are fixed electrically andmechanically by a welded connection to contact surfaces 13 that arepresent on large surfaces, facing away from one another, ofconnection-side end segment 121 of sensor element 12. Counter disk 24has a central blind hole (recess) 25, open towards the interior of thehousing, whose inner cross-section corresponds to the cross-section ofsensor element 12, so that the end of sensor element 12 is able topenetrate into blind hole 25 so as to form a positive fit with only asmall gap spacing. Blind hole 25 has a through bore (not shown) throughwhich connection-side end segment 121 of sensor element 12 is connectedto the surrounding atmosphere. Housing 11 and connecting piece 23 areconnected to one another by a weld seam 22 or a circumferentialcaulking.

A sealing piece 26 that has a central feedthrough 27 and that fills theinner cross-section of housing 11 is placed into housing 11. Cylindricalsealing piece 26 has two cylinder segments 261, 262 having differentdiameters. With its cylindrical segment 262 having the smaller diameter,sealing piece 26 is pushed without a gap into the tubular segment ofconnecting piece 23 that penetrates into housing 11, and itslarger-diameter cylindrical segment 261 presses against the inner wallof housing 11. On its end surface facing counter disk 24, sealing piece26 has two spacing elements 28 that are supported on counter disk 24, sothat in the inserted state of sealing piece 26, as shown in FIG. 2, itis ensured that only a minimal intermediate space 29 remains betweencounter disk 24 and smaller-diameter cylindrical segment 262. In thisinserted state of sealing piece 26, feedthrough 27 surrounds sensorelement 12 in the area of contact surfaces 13 and conductor elements 18,which are welded to contact surfaces 13. As is shown in FIG. 2 and FIG.3, the inner cross-section of feedthrough 27 is matched to the shape ofsensor element 12, and in this exemplary embodiment is rectangular.Feedthrough 27 tapers, beginning from the end surface of sealing piece26 facing counter disk 24, towards the end surface of sealing piece 26facing away from counter disk 24.

The assembly of the measurement sensor for creating the gas-tightextension of conductor elements 18 out of housing 11 is carried out withthe following method steps:

Connecting piece 23 with inserted counter disk 24 and conductor elements18 led through it is completely pre-assembled. Sensor element 12 isinserted into blind hole 25 of counter disk 24, and conductor elements18 protruding from counter disk 24 are welded to contact surfaces 13 onsensor element 12. Sensor element 12 and connecting piece 23 are placedinto housing 11, and housing 11 and connecting piece 23 are welded toone another. Next, a determined quantity of ceramic casting compound 31(alternatively, ceramic glue 31) is dispensed into protective tube 23,onto counter disk 24. Then sealing piece 26, pushed onto sensor element12, is pushed into the tube end of connecting piece 23 with itssmaller-diameter cylindrical segment 262. The insertion pressure firstresults in a uniform radial distribution of ceramic casting compound 31in the intermediate space 29 between sealing piece 26 and counter disk24. When intermediate space 29 is maximally filled, ceramic castingcompound 31 increasingly enters into feedthrough 27, and, as a result ofthe throttle effect of the tapered feedthrough 27, is finally pressedout from feedthrough 27 as the press-in pressure increases, at the endside of sealing piece 26 facing away from counter disk 24. The pushingof sealing piece 26 into connecting piece 23 is terminated as soon asannular shoulder 263 formed between cylindrical segments 261, 262 runsinto the annular end surface of connecting piece 23, or at the latestwhen spacing elements 28 come into contact with counter disk 24. Inorder to prevent the penetration of ceramic casting compound 31 into thegap that remains between blind hole 25 in counter disk 24 and sensorelement 12, a sealing element 32, which tightly surrounds sensor element12, is placed on the end surface of counter disk 24 facing sealing piece26. Sealing element 32 can for example be a small, round fiberglassmatting that is slit in the penetration area of sensor element 12. Ifthere is a risk that ceramic casting compound 31 will dry out due to itsconsistency, sealing piece 26 is assembled in the wet state.

1-17. (canceled)
 18. A measurement sensor for determining a physicalproperty of a measurement gas, comprising: a housing; a sensor elementaccommodated in the housing, wherein a first end segment of the sensorelement on a measurement-gas side is configured to be exposed to themeasurement gas by protruding from the housing, and wherein a second endsegment of the sensor element on a connection side has at least onecontact surface; and at least one conductor element that contacts the atleast one contact surface; wherein the at least one contact surface andthe conductor element are connected to each other by welding, andwherein, at least in an area of welded connection, the at least onecontact surface and the conductor element are embedded in an insulatingceramic compound.
 19. The measurement sensor as recited in claim 18,wherein the physical property includes one of a concentration of acomponent of the measurement gas and a temperature of the measurementgas, and wherein the welded connection between the at least one contactsurface and the at least one conductor element is formed by one ofresistance welding and laser welding.
 20. The measurement sensor asrecited in claim 18, wherein the at least one contact surface is made ofone of platinum and a platinum cermet.
 21. The measurement sensor asrecited in claim 18, wherein the at least one conductor element is madeof nickel.
 22. The measurement sensor as recited in claim 18, whereinthe insulating ceramic compound includes a compressed powder fillingthat fills a space between an inner wall of the housing and the secondend segment of the sensor element, and wherein the compressed powderfilling includes magnesium oxide.
 23. The measurement sensor as recitedin claim 18, wherein the at least one contact surface and the conductorelement are embedded in the insulating ceramic compound by pressing inthe ceramic compound, and wherein the insulating ceramic compoundincludes one of a ceramic casting compound, a ceramic glue, steatite,and aluminum oxide.
 24. The measurement sensor as recited in claim 18,wherein a first end surface of the insulating ceramic compound on aconnection side is covered by a terminating disk that is supportedperipherally on an inner wall of the housing, and wherein the at leastone conductor element extends through the terminating disk.
 25. Themeasurement sensor as recited in claim 24, wherein the housing iscrimped onto the terminating disk.
 26. The measurement sensor as recitedin claim 18, wherein a second end surface of the insulating ceramiccompound is juxtaposed by a sealing system that surrounds the sensorelement, and wherein the sealing system is supported in a gas-tightmanner on an inner wall of the housing.
 27. The measurement sensor asrecited in claim 26, further comprising: an additional insulating diskprovided on an end of the sealing system facing away from the insulatingceramic compound, wherein the additional insulating disk surrounds thesensor element and is supported on the housing.
 28. The measurementsensor as recited in claim 23, further comprising: a counter disk fixedin the housing, wherein the at least one conductor element extendsthrough the counter disk; a sealing piece that is pressed into thehousing and that fills at least a portion of the inner space of thehousing, wherein the sealing piece has a feed-through channel thatsurrounds the sensor element in the area of welded connection betweenthe at least one contact surface and the at least one conductor element;and at least one of a ceramic casting compound and a ceramic gluefilling: a) an intervening space between the counter disk and thesealing piece; and b) an intervening space between the sensor elementand a wall defining the feed-through channel.
 29. The measurement sensoras recited in claim 28, wherein the feed-through channel has across-section shape that is substantially matched to a cross-sectionshape of the sensor element, and wherein the cross-section of thefeed-through channel tapers toward an end of the sealing piece facingaway from the counter disk.
 30. The measurement sensor as recited inclaim 28, wherein the counter disk has a recess that receives the sensorelement with a positive fit.
 31. The measurement sensor as recited inclaim 28, wherein an end surface of the sealing piece facing the counterdisk has at least one axially protruding spacer element for supportingthe sealing piece on the counter disk.
 32. The measurement sensor asrecited in claim 28, further comprising: a tubular connecting piecefixedly connected to the housing, wherein one end of the tubularconnecting piece penetrating into the housing; wherein the counter diskis positioned within the tubular connecting piece at a distance from theone end of the tubular connecting piece, and wherein at least a segmentof the sealing piece is pressed into the one end of the tubularconnecting piece.
 33. The measurement sensor as recited in claim 28,wherein a further sealing element is provided on an end surface of thecounter disk facing the sealing piece, and wherein the further sealingelement also surrounds the sensor element.
 34. A method for assembling ameasurement sensor, the measurement sensor including: a housing; asensor element accommodated in the housing and having at least onecontact surface; at least one conductor element that contacts the atleast one contact surface, wherein the at least one contact surface andthe conductor element are connected to each other by welding, andwherein, at least in an area of welded connection, the at least onecontact surface and the conductor element are embedded in an insulatingceramic compound; a counter disk fixed in the housing, wherein the atleast one conductor element extends through the counter disk, andwherein the counter disk has a recess that receives the sensor element;a sealing piece that is pressed into the housing and that fills at leasta portion of the inner space of the housing, wherein the sealing piecehas a feed-through channel that surrounds the sensor element in the areaof welded connection between the at least one contact surface and the atleast one conductor element, and wherein an end surface of the sealingpiece facing the counter disk has at least one axially protruding spacerelement; and at least one of a ceramic casting compound and a ceramicglue filling a) an intervening space between the counter disk and thesealing piece, and b) an intervening space between the sensor elementand a wall defining the feed-through channel; the method comprising:fixing the counter disk in the housing, wherein the at least oneconductor element extends through the counter disk; inserting the sensorelement into the recess of the counter disk; welding the at least oneconductor element to the at least one contact surface; dispensing aquantity of at least one of the ceramic casting compound and the ceramicglue onto the counter disk that is fixed in the housing; pressing thesealing piece into the housing towards the counter disk to the extentthat the intervening space between the counter disk and the sealingpiece is filled with the at least one of the ceramic casting compoundand the ceramic glue, wherein a minimum axial depth of the interveningspace between the counter disk and the sealing piece is determined bythe at least one axially protruding spacer element.